YAY on the new shot-spot.
That's good news.
The eyes and nostrils, they're worse yes? What are you using at this point to flush them with? I'm curious if it's one thing, maybe another thing can be tried.
On the wound, how large is the actual opening at this point? Were you ever able to locate the other opening?
I'm thinking a different approach may be needed now. I think this is transitioning from a simple wound infection to being a sinus infection instead. Or some combination. Since you're transitioning into some sinus infection treatments anyway, let's explore that option more - give it more of a fight in that area as well. The penicillin will do its job on the possom bacteria.
Sinuses. I found a good article on how exactly to flush the sinus in birds. In it, they recommend a warmed saline solution. They say to press the syringe up to the nares and form a seal there, and slowly squirt the saline. It says that the fluid will come out of the choanal opening (that opening in the roof of their beak) and out of the mouth. For this, the bird must have their head lower than their body, beak pointing down. Of course, never force the flush - there should be something clogged in there.
If I were to do that, I'd clean the choanal opening first and get as much of the gunk away from it as possible. Very warm water. Honestly I'd really use VetRx for that part.
There's also the option of switching to an antibiotic that will treat her sinusitis specifically. This is one of those cases where I would consider treating with Enroxil, which is enrofloxacin which is Baytril. Baytril is the Bayer brand name.
http://www.allbirdproducts.com/newproductpages/enroxil.html is the best price and a reasonable supplier.
Baytril is a very strong drug. You'll definitely need to give probiotics while you give it. It's NOT one that I recommend ever for general illnesses because it's a "big gun" drug that you don't want to give indiscriminately. But it's killer to bad bacteria stuck up in sinuses.
The good news is that it's effective in wounds and abcesses by E. coli, Klebsiella, P. mirabilis, and the dreaded Staphylococcus. It's also good for respiratory infections. When I had a hen that was injured and prescribed antibiotics, and a cockatoo with wounds, this is what the vets gave. Just the Baytril form - in solution, syrup.
Maybe a slight change in angle of approach would get her past this plateau in the upward rise of her improvement.
In the mean time, I hope you're able to get the possom. If they do a live trap and you have to replace the bait, our possoms are really big fans of molasses on bread (or in our case, oats = horse feed). that way you won't get feral cats in the trap. It's worth a shot.. I need to do the same; a possom, or his droppings, almost killed my best horse this year and now he's still in a neurological rehabilitative process. Possoms, by the way, are also notorious carriers of the disease 'sarco' which is devestating to birds. They poop where they eat, so he'll infest your chickens' area so good riddance to him.
I hope today finds you and your gal well!